Account suddently Nil balance

Good Day, I have a uchoose 110 contract and after checking my balance this morning I had R155.95. I made an 8 minute phone call and rechecked my balance which read +-R143,00. After an hour or so, I tried to make another phone call and was told that my balance was Nil. How can that be. I phoned Customer Care and was told that my phone's data was on and it's downloading data. I tried to explain to the gentleman that we have wifi at home and that my cellular data is turned off when I'm at home but he insisted that my cellular data was on. How can R144 suddently disappear from my account within a couple of hours.